Antibodies to the most tightly bound proteins in eukaryotic DNA

DNA released from eukaryotic cells by proteases/SDS or by alkali/SDS still contains distinct proteins which are not removed by these cell lysis procedures nor by subsequent phenol treatment. The proteins most tightly bound to DNA can only be isolated by degradation of DNA. In contrast to the protein-DNA complexes, the protein material isolated after degradation of DNA is sensitive to protease treatment. Moreover, the isolated protein material tends to form aggregates which are insoluble in buffers not containing detergents. They are only poorly soluble in buffers containing SDS. The partially solubilized material can be separated by SDS-polyacrylamide gel electrophoresis into two main bands. Antibodies were raised in rabbits against the polypeptides contained in these main bands. Immunofluorescence micrographs are presented of cells treated with the antibodies. The results indicate that the proteins characterized by their involvement in extremely stable protein-DNA complexes also occur independently of DNA in eukaryotic cells.